There is a functional connection between Apolipoprotein E (ApoE) and Alzheimer's disease. The underlying biochemical mechanism by which ApoE predisposes its carriers to this disease is not known and is under debate. One model suggests that members of a family of ApoE receptors that are abundantly expressed on the surface of neurons, specifically the ApoE2 and VLDL receptors, may be involved in this pathological process. Two of these ApoE receptors, the VLDL receptor and the ApoER2, are also receptors for Reelin, a signaling protein that regulates neuronal migration during brain development. Adult expression of Reelin by GABA-ergic interneurons coupled to a high expression of ApoE2 and VLDL receptors in the hippocampus strongly suggests a role for these systems in adult CNS. The basis for this proposal is the hypothesis that there is a function of the Reelin/ApoE2/VLDL receptor system as a modulator of neurotransmission in the adult CNS. To better understand the role of this receptor system in mammalian hippocampal function, we will undertake four specific aims: [unreadable] Aim 1: Determine if mice deficient for ApoE2 and VLDL receptors exhibit deficits in learning and memory and hippocampal synoptic function. [unreadable] Aim 2: Determine the effect of Reelin application and Reelin signaling disruption on adult hippocampal synaptic transmission and plasticity. [unreadable] Aim 3: Test the hypothesis that Reelin acts through Src tyrosine kinase to phosphorylate NMDA receptors in an ApoER2/VLDL receptor-dependent manner. [unreadable] Aim 4: Determine the structure/function relationship for ApoER2 cytoplasmic domains. [unreadable] These studies will provide a basic understanding of the role for the lipoprotein receptors ApoE2 and VLDL in mammalian learning and memory mechanisms and hippocampal synaptic transmission and plasticity. Moreover, these studies will provide the first insight into the mechanisms of Reelin signaling through these receptors to modulate hippocampal function. Overall, this work will help shed light on the potential role of these ApoE receptors in neurodegenerative disorders, such as Alzheimer's disease. [unreadable] [unreadable]